Lithography is a key process in the fabrication of semiconductor integrated circuits and many optical, magnetic, biological, and micromechanical devices. Lithography creates a pattern on a substrate-supported moldable film so that, in subsequent process steps, the pattern can be replicated in the substrate or in another material that is added onto the substrate.
Conventional lithography, referred to as photolithography, involves applying a thin film of photosensitive resist to a substrate, exposing the resist to a desired pattern of radiation and developing the exposed resist to produce a physical pattern on the substrate. The resolution of patterns produced by photolithography is limited by the wavelength of the exposing radiation. Moreover, as pattern features become smaller, increasingly expensive shorter wavelength equipment is required.
Imprint lithography, based on a fundamentally different principle, offers high resolution, high throughput, low cost and the potential of large area coverage. In imprint lithography, a mold with a pattern of projecting and recessed features is pressed into a moldable surface, typically a thin film, deforming the shape of the film and forming a relief pattern in the film. The film is hardened, as by UV or thermal curing, and the mold and imprinted substrate are separated. After the mold is removed, the residual reduced thickness portions of the film can be removed to expose the underlying substrate for further processing. Imprint lithography can be used to replicate patterns having high resolution features in the microscale and nanoscale ranges. Details of nanoscale imprint lithography (“nanoimprint lithography”) are described in U.S. Pat. No. 5,772,905 issued Jun. 30, 1998 and entitled “Nanoimprint Lithography”. The '905 patent is incorporated herein by reference.
A potential limitation on the throughput of manufacturing using imprint lithography is the time required for separating the mold and the substrate. Typically, the mold and substrate are mechanically separated from the edge by inserting a wedge between the mold and substrate. This edge separation typically requires transporting the mold/substrate assembly from the pressing apparatus to the separation apparatus, thus, limiting throughput of imprinting. Furthermore, this edge separation deteriorates the mold, which, in turn, increases operation cost and limits throughput.
Accordingly, it would be highly desirable to provide improved methods and apparatus for separation in imprint lithography.